1. Field of the Invention
The invention relates to a laser range finding device and distance measurement method thereof, and more precisely, to a laser range finding device and distance measurement method for measuring a distance between a laser range finding device and a target using time of flight (TOF) of laser signals.
2. Description of the Related Art
Generally, distance measurement methods using laser signals can be classified into three types: phase, interference and pulse feedback types. For a laser range measurement with a pulse type, a distance between a laser range finding device and a target is calculated by directly measuring time of flight of the laser light pulse signal. When a laser diode is trigged by a driving circuit, it generates a start pulse as a starting signal of a time distance measurement system to start counting time. Then, after a reflected laser signal has been received and amplified, the laser diode generates a stop pulse to stop the time count. A counting circuit measures a time difference between the start pulse and the stop pulse to calculate and obtain a time of flight of the transmitted laser pulse signal from the target to the laser range finding device, thereby obtaining the distance between the laser range finding device and the target using the calculated time of flight.
However, when performing a long distance measurement (i.e., the target is far away from the laser range finding device), the signal strength of the reflected signal received by the laser range finding device may be very weak, such that the signal strength of the received signal is only a little larger than that of a noise signal. In this case, noise signal values may be erroneous determined as the target signal if a predetermined threshold level is set too small or the weak signal reflected from the target will not be detected if the predetermined threshold level is set too large.
It is therefore desired to provide methods and apparatuses for improving the ability of the distance measured for the laser range finding device.